Trans-Impedance Amplifier, Chip, and Communications Device

ABSTRACT

A trans-impedance amplifier (TIA) includes a first circuit, a second circuit, and a third circuit. Both the first circuit and the second circuit are coupled to a current source, an operational amplifier, and the third circuit. The first circuit is configured to receive a first current, provide a third voltage to the third circuit, perform shape filtering on the first current, and convert the shape filtered first current to a first voltage for output. The second circuit is configured to receive a second current, provide a fourth voltage to the third circuit, perform shape filtering on the second current, and convert the shape filtered second current to a second voltage for output. The third circuit is configured to cooperate with the first circuit and the second circuit in performing shape filtering. The operational amplifier is configured to provide a small-signal virtual ground point to the first circuit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/825,708, filed on Mar. 20, 2020, which is a continuation of U.S.patent application Ser. No. 15/894,467, filed on Feb. 12, 2018, now U.S.Pat. No. 10,637,416. The U.S. patent application Ser. No. 15/894,467claims priority to Chinese Patent Application No. 201710099963.5, filedon Feb. 23, 2017. All of the afore-mentioned patent applications arehereby incorporated by reference in their entireties.

TECHNICAL FIELD

This application relates to the field of chip technologies, and inparticular, to a trans-impedance amplifier (TIA), a chip, and acommunications device.

BACKGROUND

A TIA may be configured to convert a current signal to a voltage signal,and is widely applied to a receiving part of a sensor and a radiofrequency transceiver system.

Currently, commonly used TIAs are a TIA of a first-order activestructure is shown in FIG. 1A while a TIA of a second-order activestructure is shown in FIG. 1B. Further, the TIA of the first-orderactive structure shown in FIG. 1A includes only one operationalamplifier, and has an advantage in terms of power consumption comparedwith the TIA of the second-order active structure shown in FIG. 1B. TheTIA of the first-order active structure, however, has a lower filteringcapability. The TIA of the second-order active structure shown in FIG.1B can perform second-order shaping filtering on an input current, andtherefore has a relatively strong out-of-band interference suppressioncapability.

In conclusion, TIAs of common structures at present all have performancetradeoffs.

SUMMARY

The embodiment of the present disclosure provides a TIA, a chip, and acommunications device, that reduce power consumption of a TIA whileimproving filtering performance.

According to a first aspect, a TIA is provided, including a firstcircuit, a second circuit, a third circuit, and an operationalamplifier, where each of the first circuit, the second circuit, and thethird circuit includes a passive component. The first circuit isconnected to a current source, the operational amplifier, and the thirdcircuit, and is configured to receive a first current provided by thecurrent source, provide a third voltage to the third circuit based onthe first current, perform shaping filtering on the first current andconverting the processed first current to a first voltage for output,and provide the first voltage to the operational amplifier. The secondcircuit is connected to the current source, the operational amplifier,and the third circuit, and is configured to receive a second currentprovided by the current source, provide a fourth voltage to the thirdcircuit based on the second current, perform shaping filtering on thesecond current and converting the processed second current to a secondvoltage for output, and provide the second voltage to the operationalamplifier, where the first current and the second current provided bythe current source are two currents in a differential current. The thirdcircuit is configured to cooperate with the first circuit in performingshaping filtering on the first current and cooperate with the secondcircuit in performing shaping filtering on the second current accordingto the third voltage and the fourth voltage, and the operationalamplifier is configured to provide a small-signal virtual ground pointto the first circuit for the first current to enter the first circuit,and provide a small-signal virtual ground point to the second circuitfor the second current to enter the second circuit.

The TIA in embodiments of this application includes only one operationalamplifier, and has a smaller quantity of operational amplifiers comparedwith a TIA of a second-order active structure shown in FIG. 1B.Therefore, power consumption of the TIA in the embodiments of thisapplication is lower. In addition, the TIA in the embodiments of thisapplication includes the third circuit, and the third circuit cancooperate with the first circuit in performing shaping filtering on thecurrent in the first circuit and cooperate with the second circuit inperforming shaping filtering on the current in the second circuitaccording to the third voltage and the fourth voltage. Therefore,compared with a TIA of a first-order active structure shown in FIG. 1A,filtering performance of the TIA in the embodiments of this applicationis improved, and an out-of-band interference suppression capabilitythereof is further improved.

Based on the first aspect, in a possible design, the first circuitincludes a first part and a second part, the first part and the secondpart are connected in parallel, one end of the parallel connection isconnected to the current source and a negative input of the operationalamplifier, and the other end of the parallel connection is connected toa first output of the operational amplifier, and the first part includesat least one capacitor, and the at least one capacitor is connected inseries and/or in parallel, and the second part includes at least onefirst resistor and at least one second resistor, where the at least onefirst resistor is connected in series and/or in parallel, the at leastone second resistor is connected in series and/or in parallel, the atleast one first resistor is connected in series to the at least onesecond resistor, and a connection point of the series connection isconnected to the third circuit.

According to the foregoing manner, an implementation of the firstcircuit is simplified.

Based on the first aspect, in a possible design, the second circuitincludes a third part and a fourth part, the third part and the fourthpart are connected in parallel, one end of the parallel connection isconnected to the current source and a positive input of the operationalamplifier, and the other end of the parallel connection is connected toa second output of the operational amplifier, and the third partincludes at least one capacitor, and the at least one capacitor isconnected in series and/or in parallel, and the fourth part includes atleast one third resistor and at least one fourth resistor, where the atleast one third resistor is connected in series and/or in parallel, theat least one fourth resistor is connected in series and/or in parallel,the at least one third resistor is connected in series to the at leastone fourth resistor, and a connection point of the series connection isconnected to the third circuit.

According to the foregoing manner, an implementation of the secondcircuit is simplified.

Based on the first aspect, in a possible design, the third circuitincludes at least one capacitor, and the at least one capacitor isconnected in series and/or in parallel.

According to the foregoing manner, an implementation of the thirdcircuit is simplified. Moreover, the third circuit in the foregoingdesign can cooperate with the first circuit and the second circuit inorder to improve a filtering capability, and further improve theout-of-band interference suppression capability of the TIA.

Based on the first aspect, in a possible design, the first circuitincludes a first capacitor, a first resistor, and a second resistor, thefirst resistor and the second resistor are connected in series and thenconnected to the first capacitor in parallel, one end of the parallelconnection is connected to the current source and a negative input ofthe operational amplifier, and the other end of the parallel connectionis connected to a first output of the operational amplifier, and aconnection point of the series connection between the first resistor andthe second resistor is connected to the third circuit.

Based on the first aspect, in a possible design, the second circuitincludes a second capacitor, a third resistor, and a fourth resistor,the third resistor and the fourth resistor are connected in series andthen connected to the second capacitor in parallel, one end of theparallel connection is connected to the current source and a positiveinput of the operational amplifier, and the other end of the parallelconnection is connected to a second output of the operational amplifier,and a connection point of the series connection between the thirdresistor and the fourth resistor is connected to the third circuit, andthe first capacitor and the second capacitor have a same capacitance,and resistances of the first resistor, the second resistor, the thirdresistor, and the fourth resistor are the same.

Based on the first aspect, in a possible design, the third circuitincludes a third capacitor, and the third circuit has a same capacitanceas the first capacitor and the second capacitor.

According to a second aspect, a chip is provided, including the TIA inany possible design provided in the first aspect.

According to a third aspect, a communications device is provided,including the chip provided in the second aspect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows a TIA of a first-order active structure;

FIG. 1B shows a TIA of a second-order active structure;

FIG. 2 is a schematic structural diagram of a TIA according to anembodiment of this application;

FIG. 3A and FIG. 3B are schematic structural diagrams of a first circuitaccording to an embodiment of this application;

FIG. 4A and FIG. 4B are schematic structural diagrams of a secondcircuit according to an embodiment of this application;

FIG. 5 is a schematic structural diagram of a third circuit according toan embodiment of this application;

FIG. 6 is a schematic structural diagram of a TIA according to anembodiment of this application; and

FIG. 7 is a comparison diagram of amplitude-frequency characteristiccurves of a TIA in an embodiment of this application and a TIA of afirst-order active structure.

DESCRIPTION OF EMBODIMENTS

The term “and/or” in the embodiments of this application describes onlyan association relationship for describing associated objects andrepresents that three relationships may exist. For example, A and/or Bmay represent the three cases, namely: only A exists, both A and Bexist, and only B exists. In addition, the character “/” in theembodiments of this application generally indicates an “or” relationshipbetween the associated objects.

The following further describes the embodiments of this application indetail with reference to the accompanying drawings.

A TIA is configured to convert a current signal to a voltage signal, andmay be integrated into a chip and applied in a communications device,for example, applied to a receiving part of a sensor in thecommunications device or applied in a radio frequency transceiver systemof the communications device.

A TIA in the embodiments of this application includes only oneoperational amplifier, and has a smaller quantity of operationalamplifiers compared with a TIA of a second-order active structure shownin FIG. 1B. Therefore, power consumption of the TIA in the embodimentsof this application is lower. In addition, the TIA in the embodiments ofthis application includes a third circuit, and the third circuit cancooperate with a first circuit in performing shaping filtering on acurrent in the first circuit, and cooperate with a second circuit inperforming shaping filtering on a current in the second circuitaccording to the third voltage and the fourth voltage. Therefore,compared with a TIA of a first-order active structure shown in FIG. 1A,filtering performance of the TIA in the embodiments of this applicationis improved, and an out-of-band interference suppression capabilitythereof is further improved.

As shown in FIG. 2, a TIA 200 in an embodiment of this applicationincludes a first circuit 210, a second circuit 220, a third circuit 230,and an operational amplifier 240. Each of the first circuit 210, thesecond circuit 220, and the third circuit 230 includes a passivecomponent.

The first circuit 210 is connected to a current source, the operationalamplifier 240, and the third circuit 230, and is configured to receive afirst current provided by the current source, provide a third voltage tothe third circuit 230 based on the first current, perform shapingfiltering on the first current and converting the processed firstcurrent to a first voltage for output, and provide the first voltage tothe operational amplifier 240.

A first end 211 of the first circuit 210 is connected to one end of thecurrent source and a negative input 241 of the operational amplifier240, a second end 212 of the first circuit 210 is connected to a firstoutput 242 of the operational amplifier 240, and a third end 213 of thefirst circuit 210 is connected to one end 231 of the third circuit 230.The first circuit 210 is configured to receive the first currentprovided by the current source using the first end 211, provide thethird voltage to the end 231 of the third circuit 230 based on the firstcurrent, perform shaping filtering on the first current and convertingthe processed first current to the first voltage, and output the firstvoltage using the second end 212. Because the second end 212 of thefirst circuit 210 is connected to the first output 242 of theoperational amplifier 240, a voltage of the first output 242 is set tothe first voltage.

The second circuit 220 is connected to the current source, theoperational amplifier 240, and the third circuit 230, and is configuredto receive a second current provided by the current source, provide afourth voltage to the third circuit 230 based on the second current,perform shaping filtering on the second current and converting theprocessed second current to a second voltage for output, and provide thesecond voltage to the operational amplifier 240. The first current andthe second current provided by the current source are two currents in adifferential current.

A first end 221 of the second circuit 220 is connected to the other endof the current source and a positive input 243 of the operationalamplifier 240, a second end 222 of the second circuit 220 is connectedto a second output 244 of the operational amplifier 240, and a third end223 of the second circuit 220 is connected to the other end 232 of thethird circuit 230. The second circuit 220 is configured to receive thesecond current provided by the current source using the first end 221 ofthe second circuit 220, provide the fourth voltage to the other end 232of the third circuit 230 based on the second current, perform shapingfiltering on the second current and converting the processed secondcurrent to the second voltage, and output the second voltage using thesecond end 222. Because the second output 244 of the operationalamplifier 240 is connected to the second end 222, a voltage of thesecond output 244 is set to the second voltage by the second circuit220.

The third circuit 230 is configured to cooperate with the first circuit210 in performing shaping filtering on the first current and cooperatewith the second circuit 220 in performing shaping filtering on thesecond current according to the third voltage and the fourth voltage.

The operational amplifier 240 is configured to provide a small-signalvirtual ground point to the first circuit 210 for the first current toenter the first circuit 210, and provide a small-signal virtual groundpoint to the second circuit 220 for the second current to enter thesecond circuit 220.

The operational amplifier 240 is configured to provide the small-signalvirtual ground points to the first circuit 210 and the second circuit220, respectively.

The operational amplifier 240 provides the small-signal virtual groundpoint to the first end 211 of the first circuit 210 using the negativeinput 241 to make a voltage of the first end 211 set to zero such thatthe first current provided by the current source enters the firstcircuit 210. The operational amplifier 240 provides the small-signalvirtual ground point to the first end 221 of the second circuit 220using the positive input 243 to make a voltage of the first end 221 setto zero such that the second current provided by the current sourceenters the second circuit 220.

It should be understood that, the passive component includes a componentsuch as a capacitor, an inductor, and a resistor. Passive components maybe used to form the first circuit 210, the second circuit 220, and thethird circuit 230 to implement functions in this embodiment of thisapplication. A quantity and type of the passive components are notlimited herein.

In a possible design, the first circuit 210 includes a first part and asecond part, the first part and the second part are connected inparallel, one end (that is, the first end 211) of the parallelconnection is connected to the current source and the negative input 241of the operational amplifier 240, and the other end (that is, the secondend 212) of the parallel connection is connected to the first output 242of the operational amplifier 240.

The first part includes at least one capacitor, and the at least onecapacitor is connected in series and/or in parallel. The second partincludes at least one first resistor and at least one second resistor,where the at least one first resistor is connected in series and/or inparallel, the at least one second resistor is connected in series and/orin parallel, the at least one first resistor is connected in series tothe at least one second resistor, the at least one first resistor isconnected in series to the at least one second resistor, and aconnection point of the series connection is connected to the thirdcircuit 230. Further, the connection point of the series connection isconnected to the end 231 of the third circuit 230, and the connectionpoint of the series connection is the third end 213 of the first circuit210.

For example, in a first circuit 210 shown in FIG. 3A, a first partincludes three capacitors C1, C2, and C3, and a second part includes afirst resistor R1 and a second resistor R2. In a first circuit 210 shownin FIG. 3B, a first part includes a capacitor C1, and a second partincludes a first resistor R1, a first resistor R2, and a second resistorR3. In addition to connection manners of the first circuit 210 shown inFIG. 3A and FIG. 3B, for the first circuit 210 in this embodiment ofthis application, there may be another connection manner equivalent tothose in FIG. 3A and FIG. 3B.

In a possible implementation, for example, the second circuit 220includes a third part and a fourth part in parallel, one end (that is,the first end 221) of the parallel connection is connected to thecurrent source and the positive input 243 of the operational amplifier240, and the other end (that is, the second end 222) of the parallelconnection is connected to the second output 244 of the operationalamplifier 240.

The third part includes at least one capacitor, and the at least onecapacitor is connected in series and/or in parallel. The fourth partincludes at least one third resistor and at least one fourth resistor,where the at least one third resistor is connected in series and/or inparallel, the at least one fourth resistor is connected in series and/orin parallel, the at least one third resistor is connected in series tothe at least one fourth resistor, and a connection point of the seriesconnection is connected to the third circuit 230. Further, theconnection point of the series connection is connected to the other end232 of the third circuit 230, and the connection point of the seriesconnection is the third end 223 of the second circuit 220.

For example, in a second circuit 220 shown in FIG. 4A, a third partincludes four capacitors C1, C2, C3, and C4, and a fourth part includesa third resistor R1 and a fourth resistor R2. In a second circuit 220shown in FIG. 4B, a third part includes a capacitor C1, and a fourthpart includes a third resistor R1, a third resistor R2, and a fourthresistor R3. In addition to connection manners of the second circuit 220shown in FIG. 4A and FIG. 4B, for the second circuit 220 in thisembodiment of this application, there may be another connection mannerequivalent to those in FIG. 4A and FIG. 4B.

It should be understood that, the connection manners of the firstcircuit 210 and the second circuit 220 may be the same or may bedifferent, and a quantity of capacitors and quantities of firstresistors, second resistors, third resistors, and fourth resistors inthe first circuit 210 and the second circuit 220 are not limited.

In a possible design, the third circuit 230 includes at least onecapacitor, and the at least one capacitor is connected in series and/orin parallel.

For example, if the third circuit 230 includes two capacitors C1 and C2,as shown in FIGS. 5, C1 and C2 are connected in parallel in the thirdcircuit 230. One end of the third circuit 230 is connected to the thirdend 213 of the first circuit 210, and the other end of the third circuit230 is connected to the third end 223 of the second circuit 220. Itshould be understood that, a quantity of capacitors included in thethird circuit 230 is not limited in this embodiment of this application.

It should be noted that, in this embodiment of this application, aresistance and a capacitance may be set according to an actual need, toobtain a required voltage.

The following uses a TIA shown in FIG. 6 as an example and assumes thata gain of an operational amplifier within an operating frequency rangeis infinite to perform qualitative analysis on the TIA in theembodiments of this application using a small-signal equation.

As shown in FIG. 6, the TIA includes capacitors C1, C2, and C3,resistors R1, R2, R3, and R4, and an operational amplifier. A currentsource provides a differential current to the TIA, C1, R1, and R2 form afirst circuit, C3 forms a third circuit, and C2, R3, and R4 form asecond circuit. A current of the differential current flows into thefirst circuit through p1, and the other current of the differentialcurrent flows into the second circuit through n1.

A negative input of the operational amplifier provides a small-signalvirtual ground point to the first circuit, and a positive input of theoperational amplifier provides a small-signal virtual ground point tothe second circuit. It is assumed that voltages at a point a, a point b,a point p2, and a point n2 shown in FIG. 6 are Va, Vb, Vp, and Vn,respectively, a current that the current source provides to the firstcircuit is i1, and a current that the current source provides to thesecond circuit is i2, a sum of currents that flow through the point a,the point b, a point c, and a point d respectively is zero. In thiscase, the following formulas are obtained:

$\begin{matrix}{{{{( {{Va} - 0} )/R}\; 1} + {{( {{Va} + {Vp}} )/R}\; 2} + {( {{Va} - {Vb}} )/\frac{1}{j\;\omega\; C\; 3}}} = 0} & (1) \\{{{{( {{Vb} - 0} )/R}\; 3} + {{( {{Vb} + {Vn}} )/R}\; 4} + {( {{Vb} - {Va}} )/\frac{1}{j\;\omega\; C\; 3}}} = 0} & (2) \\{{{{- i}\; 1} + {{( {0 - {Va}} )/R}\; 1} + {( {0 - {Vp}} )/\frac{1}{j\;\omega\; C\; 1}}} = 0} & (3) \\{{{{{- i}\; 2} + {{( {0 - {Vb}} )/R}\; 3} + {( {0 - {Vn}} )/\frac{1}{j\;\omega\; C\; 2}}} = 0},} & (4)\end{matrix}$

where ω indicates an operating frequency, when R1=R2=R3=R4=R andC1=C2=C3=C, a transfer function is obtained as follows:

$\frac{Vout}{Iin} = {\frac{{Vp} - {Vn}}{{i\; 1} - {i\; 2}} = {\frac{2{R( {1 + {{R \cdot C \cdot j}\;\omega}} )}}{1 + {2{R \cdot C \cdot j}\;\omega} + {2{R^{2} \cdot C^{2} \cdot ( {j\;\omega} )^{2}}}}.}}$

It can be learned from the transfer function that, the transfer functionincludes two poles and one zero, and the zero and one pole form azero-pole pair on a near passband. Compared with a first-order active RCstructure, in-band flatness of the TIA in the embodiments of thisapplication is improved. If a same 3 decibels (dB) corner frequency isused, the TIA in the embodiments of this application has a betterout-of-band suppression characteristic compared with a TIA of afirst-order active structure. As shown in FIG. 7, a curve 1 is anamplitude-frequency characteristic curve when R1=R2=R3=R4=R andC1=C2=C3=C, while a curve 2 is an amplitude-frequency characteristiccurve of a TIA that is of a first-order active structure and to which C3is not added. It can be learned from FIG. 7 that, the TIA in theembodiments of this application has a second-order characteristic on anear passband and has better flatness. In FIG. 7, 3 dB cornerfrequencies of the curve 1 and the curve 2 are different. The 3 dBcorner frequency of the curve 1 is A, and the 3 dB corner frequency ofthe curve 2 is B. If the TIA in the embodiments of this application hasa same 3 dB corner frequency requirement as the TIA of the first-orderactive structure, the amplitude-frequency characteristic curve in theembodiments of this application has a better out-of-band suppressioncharacteristic. In addition, the TIA in the embodiments of thisapplication uses only one operational amplifier such that powerconsumption of the TIA is reduced compared with a TIA of a second-orderactive structure.

In addition, the embodiments of this application further provide a chip,including any TIA provided in the embodiments of this application.

The embodiments of this application further provide a communicationsdevice, including the chip provided in the embodiments of thisapplication.

For a connection manner of a TIA in the chip or in the communicationsdevice, refer to the connection manner of the TIA shown in FIG. 2.Details are not described herein.

Although some specific embodiments that can be implemented have beendescribed, persons skilled in the art can make changes and modificationsto these embodiments once they learn the basic inventive concept.Therefore, the following claims are intended to be construed to coverthe embodiments described in this application and all changes andmodifications falling within the scope of this application.

Obviously, persons skilled in the art can make various modifications andvariations to this application without departing from the spirit andscope of this application. This application is intended to cover thesemodifications and variations of this application provided that they fallwithin the scope of protection defined by the following claims and theirequivalent technologies.

1. An integrated circuit comprising: an amplifier comprising: a pair ofinputs comprising a first input and a second input; a first resistor; asecond resistor, wherein the first resistor and the second resistor aredisposed in series and coupled to the first input; a third resistor; afourth resistor, wherein the third resistor and the fourth resistor aredisposed in series and coupled to the second input; a first capacitorcomprising: a first end coupled to a first point between the firstresistor and the second resistor; and a second end coupled to a secondpoint between the third resistor and the fourth resistor; a secondcapacitor disposed in parallel with the first resistor and the secondresistor, and coupled to the first input; a third capacitor disposed inparallel with the third resistor and the fourth resistor, and coupled tothe second input; and output for producing an amplified output from theamplifier.
 2. The integrated circuit of claim 1, wherein the amplifieris an operational amplifier.
 3. The integrated circuit of claim 1,further comprising a current source configured to provide thedifferential signal to the amplifier.
 4. The integrated circuit of claim1, wherein the amplifier comprises an output, the output is coupled tothe second capacitor.
 5. The integrated circuit of claim 1, wherein theamplifier comprises a first output and a second output, the first outputis coupled to the second capacitor, and the second output is coupled tothe third capacitor.
 6. The integrated circuit of claim 1 wherein thefirst and second inputs are coupled to receive a current signal from thepair of inputs and wherein the amplifier is a transimpedance amplifierconfigured to amplify a current signal.
 7. An integrated circuitcomprising: an amplifier comprising: a pair of inputs comprising a firstinput and a second input; a first resistor; a second resistor, whereinthe first resistor and the second resistor are disposed in series andcoupled to the first input; a first capacitor comprising: a first endcoupled to a first point between the first resistor and the secondresistor; and a second end coupled to the second input; a secondcapacitor disposed in parallel with the first resistor and the secondresistor, and coupled to the first input; and output for producing anamplified output from the amplifier.
 8. The integrated circuit of claim7, wherein the amplifier comprises an output, and the first resistor andthe second resistor bridge are disposed over the amplifier and betweenthe first input and the output.
 9. The integrated circuit of claim 7,wherein the integrated circuit comprising a third resistor and a fourthresistor, the third resistor and the fourth resistor are disposed inseries and coupled to the second input.
 10. The integrated circuit ofclaim 7, wherein the integrated circuit is a transimpedance amplifierconfigured to amplify a current signal received at the pair of inputs.